The possible regulation of gene transcription by non-histone chromosomal proteins will be examined by injecting such labelled proteins directly into mouse eggs. The movement of the labelled proteins from cytoplasm to nucleus and to the chromatin will be monitored by autoradiography. Possible effects on enzyme synthesis due to altered gene function will be examined by the use of isozymic markers. Homozygous diploid mice will be produced by microsurgical removal of one of the pronuclei in a fertilized egg. The resulting haploid embryo will then be diploidized with cytochalasin B and cultivated in vitro to the blastocyst stage. Such embryos will then be transplanted into hormonally prepared recipient female mice and carried to term. The birth of such homozygous mice should greatly accelerate the production of inbred strains and be of considerable practical utility.